In recent years, semiconductor integrated circuits have been rendered finer and more integrated.
Photolithography is frequently used as a patterning technique for semiconductors. Finer patterns based on the photolithography, however, cannot go beyond the diffraction limit of exposing light.
Thus, a nanoimprint method has been proposed for further promoting finer and higher precision circuits. The nanoimprint method refers to a thin film patterning technique that involves pressing a mold having a fine elevation/depression pattern against a substrate coated with a thin resin film to transfer the elevation/depression pattern in the mold to the thin resin film coating the substrate.
Among the nanoimprint methods, a photo-nanoimprint method disclosed in, for example, NPL 1 has received attention. The photo-nanoimprint method involves: impressing a mold transparent to exposing light onto a photocurable composition coating a substrate; curing the photocurable composition by light irradiation; and demolding the mold from the resulting cured product to produce a fine resist pattern-integrated substrate.
However, some problems should be solved for using the photo-nanoimprint method. One of the problems is that force required for releasing a mold from a cured product, i.e., mold release force, is large. Due to this large mold release force, the photo-nanoimprint method has disadvantages such as pattern defects and the reduced precision of alignment between a mold and a substrate resulting from the coming off of the substrate from the stage.
In response to such problems, PTL 1 discloses a photocured product for imprint, including a deep part disposed on the substrate side and a surface part disposed on the deep part, the surface part having a higher content of a fluorine compound than that of the deep part. Alternatively, PTL 2 discloses a photocurable composition for photo-imprint, including at least one polymerizable monomer, a photopolymerization initiator, and a fluorine atom-containing surfactant.
The photocured product disclosed in PTL 1 is intended to decrease surface energy by means of the fluorine compound contained in the surface part, thereby reducing mold release force produced during the demolding of a mold from the photocured product. Also, PTL 2 is intended to reduce mold release force under principles similar to those of PTL 1 using the photocurable composition containing the fluorine atom-containing surfactant. Unfortunately, the photocurable resin compositions disclosed in PTL 1 and PTL 2 are not sufficiently effective for reducing the mold release force.